1. Field of the Invention
This invention relates to a system of measuring tissue pressure in muscle compartments and other regions in humans and other animals. The system of this invention provides for obtaining absolute measurement values and changes in measured values with time and is useful in the diagnosis of muscle tissue compartment syndromes, tissue responses to vascular ischemia, and any disease or condition which involves increases in tissue or fluid pressure.
Specifically, this invention will be useful in the diagnosis and management of muscle compartment syndromes. For an article on acute compartment syndromes, reference is made to J. Bone Joint Surg., 60A: 1091-1095, 1978. In general, these conditions arise as a result of the trauma; frequently from fractures of the lower extremity. After such an injury, the anterior compartment and/or other compartments of the leg may swell. The increased intercompartmental pressure caused by the tissue edema and accumulation of interstitial fluid raises the compartmental pressure above venous levels which occludes venous outflow or drainage from the compartment. With this occlusion, intercompartmental pressure rises further. When the compartmental pressure rises above normal, (pressure of approximately 0 to 30 mm Hg) functional capillary flow through the capillary beds stops. At this point, oxygen and fresh nutrients are not provided to the muscles, neural and other tissues in the compartment. Widespread tissue ischemia begins and with time, tissue necrosis occurs. This point is generally reached at a compartment pressure of approximately 35 to 45 mm of mercury. With early tissue necrosis, the pressure continues to rise. The end result can be a great loss of muscle and other tissues within the involved compartment and the loss of associated function for the individual.
2. Prior Art
The traditional method of compartment syndrome diagnosis includes an observation of blood availability to the most distal parts of the extremity, the fingers and toes. The return of a pink color after pressure application to the distal parts was believed to indicate a satisfactory blood supply. The presence of pulses in the distal small arteries was thought to be a favorable factor. Pain, particularly on passive motion of the finger or toes; the observation of gross limb swelling; and "woody" feeling of the involved limb are classic positive diagnostic criteria.
In 1975, Whitesides, Haney and Morimoto described the use of a syringe, monometer, intravenous tubing, and open hypodermic needle to measure suspect compartment pressure. It was published in Clin. Orthop., 113; 43-51. Another system developed for determining the pressure within a tissue which is called the "wick catheter" and was reported by Mubarak, et al J. Bone Joint Surg., 58A; 1016-1020, 1976. Mubarak, et al used a simple manometric system and used a catheter containing a fibrous material which protrudes slightly outside the catheter itself. This was meant to push away muscle tissue and prevent occlusion of the catheter with changes in pressure. Because of the continued difficulty with occlusion and clogging of the devices used in the Whiteside system and in the Mubarak system, a "slit catheter" compartment pressure measuring device was developed by Rorabeck, et al Canad. J. Surg., 15: 249, 1972.
The devices and techniques just described in general have improved the clinicians ability to diagnose compartment criteria. However, they are not without shortcomings. For example, the method of observation of capillary refill of distal pulses and other observations of distal blood flow, fail to account for the fact that there are usually several arterial supplies to the distal limb. There can be complete necrosis of a given compartment in the face of continuous presence of pulsatile distal blood flow. In addition, a major artery passing through an involved compartment contains blood at pressures generally over 100 mm of mercury. Whereas, on the other hand, a compartment pressure in excess of the danger zone, approximately 40 mm of mercury, could cause complete tissue necrosis and never impede pulsatile blood flow through the major artery. Pain and swelling occur with many injuries to the extremeties and are very subjective. The subjective nature of pain, swelling and a feeling of "woodiness" do not help in the discrimination of a compartment syndrome or tissue ischemia with swelling as compared to a contused or otherwise traumatized limb.
The hypodermic needle manometer technique for measurement of intracompartmental pressures, has several significant disadvantages. The muscle and other tissues within a compartment are not comparable to liquids. They more closely approximate a gel. Standard hydrostatic techniques cannot suffice in the measurement of such tissue pressures. With any reversed flow, there is occlusion of the tip of the needle by muscle or other tissue. Great excesses of pressure are required to free the catheters. No accurate pressure determination can be obtained under these circumstances. Repeated measurements by the same or different observers may, at times, provide substantially different measurement values within the range of clinical interest. Further, this type of device cannot be used effectively for continuous monitoring of compartment pressures since sterile saline or other liquid fluids must repeatedly be injected into the tissue. An injection of liquid into a closed compartment, in principal, raises the pressure in that compartment and could cause an increase in severity and extent of tissue necrosis and limb injury.
While the protruding wick, the slits, mentioned above help somewhat in preventing occlusion of the catheters by muscle and other tissues, these designs have not satisfactorily eliminated this problem. They all share the problem of introduction of additional liquid into an already swollen muscle compartment and with repeated usage, increase the danger of aggravating the condition. The reproducibility and accuracy of measurements made with these systems continue to be somewhat limited.